Information content in reflected global navigation satellite system signals

The direct signals from satellites in global satellite navigation satellites systems (GNSS) as, GPS, GLONASS and GALILEO, constitute the primary source for positioning, navigation and timing from space. But also the reflected GNSS signals contain an important information content of signal travel times and the characteristics of the reflecting surfaces and structure. Ocean reflected signals from GNSS satellite systems reveal the mean height, the significant wave height and the roughness of the ocean. The estimated accuracy of the average surface height can be as low as 10 cm. For low elevations, the signals reveal the incoherent scatter process at the reflection zone. By using open-loop high-precision GNSS receivers, it is possible to provide the in-phase and quadrature components of the signal at high sample rates, which enables investigation of the spectral signatures of the observations. The retrieval method consists of a radio occultation technique for the phase differences between the direct and reflected signal combined with a statistical method. Results are derived through a sequential Bayesian estimation method, where the retrieval algorithms are based on a particle filtering technique. The horizontal size of the probability density function, which uniquely describes the ocean reflection zone using the recursive particle filter method, totals from 200 to 500 meters for all data sets.